The Best Aquarium (and Fish Tank) Rocks

Whether you’re setting up a new aquarium for the first time or adding to your existing one, aquarium and fish tank rocks add character and decoration to your tank. Rocks also greatly benefit the underwater life, both in fresh water and salt water. They provide a better environment for your fish, while creating a pleasant visual experience for you.

We looked at dozens of aquarium and fish tank rocks, both real and fake, to find the best rocks available. We looked at smooth stones, slate, cave stones, mountain rocks, and more. We noted the size, coloring, features, and price.

Best Aquarium Rock Overall
Nature's Ocean 12-Inch Coral Base Rocks for Aquarium – 40 Pounds
Nature’s Ocean coral rocks are 100 percent natural aragonite, which can be used as-is or broken down into smaller rocks.

We chose Nature’s Ocean 12-Inch Coral Base Rocks for Aquarium that comes in 40 pounds as the best overall pick due to high reviews for value and presentation. Nature’s Ocean offers 40 pounds of coral rock for your saltwater tank. Contents may vary, but customers report different weights and size rocks.

The 5 Top-Rated Aquarium (and Fish Tank) Rocks

Editor's PicksBrandRating
Best Aquarium Rock OverallNature's Ocean 12-Inch Coral Base Rocks for Aquarium – 40 Pounds4.3
Best Slate Rock for AquariumsSmall World Slate & Stone Natural Slate Stone Rocks for Aquariums4.6
Best Budget Aquarium RockVORCOOL Aquarium Sea Rock Cave Ornament for Fish Tank4.1
Best Mountain Stone for AquariumsEHC Skull Mountain Aquarium Ornament Fish Tank4.4
Best Aquarium Rock CavePenn-Plax Reptology Shale Step Ledge for Aquariums & Terrariums4.1

*Ratings are from Amazon at the time of publication and can change

Best Aquarium Rock Overall: Nature’s Ocean 12-Inch Coral Base Rocks for Aquarium – 40 Pounds

Nature’s Ocean 12-Inch Coral Base Rocks for Aquarium in the 40-pound size offers 100 percent natural aragonite rock for your saltwater sanctuary. Help filter your tank while adding numerous bacteria and algae to aid in the overall health of your underwater environment. This live rock is porous, and sports numerous natural holes and crevices for filtering the water and growing bacteria.

Nature’s Ocean base rocks can be used to create a coral base or added to an existing one. Though it is soaked in well water to prevent leaching, customers recommend thoroughly rinsing the coral stone before placing it in your tank. However, the rock will adapt quickly to the cycle of your aquarium.

Advertised as two large rocks approximately 12 inches to 17 inches in diameter, customers report the number and sizes of the rocks vary. The coral rocks can be broken down into smaller pieces to fit your tank or be arranged to create a unique rock formation when you stack them together.

Nature’s Ocean 12-Inch Coral Base Rocks for Aquarium Key Features:

  • Soaked in water to prevent leaching
  • Natural holes and crevices
  • Quickly adapts to the cycling of your tank
  • Break into smaller pieces to create your own structures

Best Slate Rock for Aquariums: Small World Slate & Stone Natural Slate Stone Rocks for Aquariums

Best Slate Rock for Aquariums
Small World Slate & Stone Natural Slate Stone Rocks for Aquariums
Build an aquascape for your fish using varying sizes of slate stone, which can be piled together to form different structures.

For the best slate rock for aquariums, we chose Small World Slate & Stone Natural Slate Stone Rocks for Aquariums. A product of the USA, these stones vary in size, shape, and texture. Slate stones will naturally become darker when wet, and display different color striations throughout the rock. White quartz and brownstone may also be included in the mix.

Safe for salt and freshwater, this slate stone will last longer than man-made materials. The mix features rocks from 3 inches to 5 inches, allowing you to build and customize your own underwater rock formation. For the heat-loving pet, these stones naturally hold heat well. Arrange the slate pieces to form caves, ledges, or mountains using aquarium-safe glue.

Small World Slate & Stone Natural Slate Stone Rocks for Aquariums Key Features:

  • 5 pounds of 3-inch to 5-inch stones
  • Sourced in the USA
  • Naturally holds heat
  • Create caves or cliffs

Best Budget Aquarium Rock: VORCOOL Aquarium Sea Rock Cave Ornament for Fish Tank

Best Budget Aquarium Rock
VORCOOL Aquarium Sea Rock Cave Ornament for Fish Tank
Safe for both saltwater and freshwater tanks, this rock cave gives your fish a place to hide out.

Our best budget buy pick is VORCOOL Aquarium Sea Rock Cave Ornament for Fish Tank for its versatile cave structure. Made out of resin, and safe for both freshwater and saltwater aquariums, this almost 5-inch tall cave is made to look like real rock. Your fish or marine life will benefit from the added interaction in their environment. It also gives them a place to swim through or hide out in.

This cave rock ornament blends easily with a myriad of underwater atmospheres and is painted to have a mossy appearance. Decorative for you to look at, but also beneficial for fish that prefer to keep secluded. The item is lightweight but stays in place. Customers claim their beta fish love the addition of the cave to their aquariums.

VORCOOL Aquarium Sea Rock Cave Ornament for Fish Tank Key Features:

  • Made from resin
  • Approximately 4 inches by 5 inches
  • For fresh and saltwater
  • One solid piece

Best Mountain Stone for Aquariums: EHC Skull Mountain Aquarium Ornament Fish Tank

Best Mountain Stone for Aquariums
EHC Skull Mountain Aquarium Ornament Fish Tank
For both freshwater and saltwater tanks, this skull mountain is made from resin, and provides your fish with a spot to hide out.

The best mountain stone for aquariums is EHC Skull Mountain Aquarium Ornament Fish Tank. Measuring just over 5 inches by just under 6 inches, this realistic-looking mountain features skulls on both sides, with a wide-mouthed cave. Made from resin with hand-painted detail, this mountain stone is safe for freshwater and marine aquariums. The material is non-toxic, as is any coloring used.

Dress up your underwater landscaping while giving your fish a place to retreat to and hang out in. The cave can be placed near plants or other aquascaping items to create a spooky atmosphere. Or use it in conjunction with other underwater structures to customize your theme. Either way, this skull mountain adds décor and finish to a myriad of aquariums.

EHC Skull Mountain Aquarium Ornament Fish Tank Key Features:

  • About 5 inches by 5 inches by 6 inches
  • Hand-painted detail
  • Double-sided skulls

Best Aquarium Rock Cave: Penn-Plax Reptology Shale Step Ledge for Aquariums & Terrariums

Best Aquarium Rock Cave
Penn-Plax Reptology Shale Step Ledge for Aquariums & Terrariums
Decorate your aquarium with the Penn-Plax shale rock cave with ledge.

Who doesn’t like a cave? Our favorite aquarium rock cave is Penn-Plax Reptology Shale Step Ledge for Aquariums & Terrariums because it doesn’t just have a cave, it has ledges too. Made to look like real stone, this hand-painted piece matches an array of decorative ideas. The fake stone steps entice all types to climb and explore, while the three different size openings allow fish to swim in and out in a variety of ways.

At 9 inches across, 7 inches deep, and nearly 4 inches tall, the Penn-Plax ledge and cave creates an out-of-the-way spot for your fish. It can hide out under the mountain or swim straight through. The top opening is 2.5 inches wide and 1.5 inches tall. Made for dry or wet habitats, this cave ledge is also safe for freshwater or marine tanks.

Penn-Plax Reptology Shale Step Ledge for Aquariums & Terrariums Key Features:

  • Hand-painted mossy design
  • Cave has three openings
  • Critters can climb and explore
  • For salt and freshwater

Who Should Buy an Aquarium (and Fish Tank) Rock

Your fish, shrimp, reptiles, and turtles deserve an interactive environment to give them mental and physical stimulation. Underwater life, just like land life, needs enrichment to live a long, fulfilling existence. Aquarium and fish tank rocks do more than just decorate your underwater landscape. They provide shelter, minerals, coral, and beneficial bacteria, as well as adjust the pH balance, for your freshwater or marine life.

Adding rocks to your aquarium or fish tank brings vibrancy and visual appeal to your aquascape, creating an inviting atmosphere for you and your fish. And depending on your style and motif, there are a number of different rock types to fit different themes.

Best Aquarium Rock Overall
Nature's Ocean 12-Inch Coral Base Rocks for Aquarium – 40 Pounds
Nature’s Ocean coral rocks are 100 percent natural aragonite, which can be used as-is or broken down into smaller rocks.

Important Features to Consider

An aquarium rock should have a few important features. Here’s what to consider when selecting an aquarium (and fish tank) rock:

  • Freshwater or saltwater? Many aquarium and fish tank rocks are made for both freshwater and saltwater tanks. But it’s important to make that determination before placing a rock in your aquarium. If the rock is not made specifically for the type of water you are using, it could throw off the pH or hardness of the water, and harm your fish.
  • The size of the tank. Consider the size of your aquarium before you choose a rock. Your underwater life needs room to move around, swim, and keep a respectable distance from other underwater life, if necessary. And though you want to make sure the rock is not too big for the tank, also consider the size of the rock for the size of your fish. If you have multiple fish, consider getting multiple sizes of rocks to accommodate all of your fish.
  • Purpose and additional features. Once you have narrowed down your choice of rock to the type of water and size tank you have, consider which type of rock will be best for your underwater life. With a variety of rocks to choose from, such as mountains, caves, dragon stone, slate, mineral balls, and smooth river rocks, connecting the right type of rock to your fish not only benefits your aquascape but will give your fish the right type of environment to optimize its health.

Frequently Asked Questions

What rocks are safe to put in an aquarium?

Though it might seem you could put any rock you want in your aquarium, that’s not really advisable. Fresh and saltwater each have different requirements to keep your fish and underwater life healthy. Some rocks, depending on the material, can alter the pH or hardness of the water. And it’s important that aquarium rocks are in line with what your fish need.

Good rocks to use for a freshwater aquarium include slate stone, lava rocks, river rocks, quartz, basalt, and shale. Do not use high salt or high calcium stone, such as limestone and marble, or shells or corals. These will alter the pH and hardness of the freshwater.

For saltwater tanks, good rocks to use include live and dead reef rocks, and petrified coral, which help filter the saltwater, and contribute good bacteria and other life.

How do I make sure rocks are safe for my aquarium?

Choose rocks that are naturally safe for your aquarium. Thoroughly rinse off a rock or stone before adding it to your tank. Do not use rocks from outside or from the ocean unless you have tested it first. Even then, it is not advisable due to unwanted bacteria and pesky hitchhikers. Test a stone by dropping a little vinegar on the rock. If it fizzes, the rock contains calcium and could alter the pH of your water. Or submerge the rock in water for an extended period of time, testing the pH along the way to see if it changes.

Can you put rocks from the ocean in a freshwater tank?

It’s not advisable to place ocean rocks in your freshwater tank unless you’re sure it won’t alter the pH or hardness of the water. Shells and crushed coral often push the pH and calcium levels too high for a freshwater aquarium. You also run the risk of introducing foreign bacteria to your tank.

What rocks raise pH in an aquarium?

Limestone will cause the pH of the water to rise, and also harden the water, due to its calcareous nature – meaning it contains calcium. Likewise, any rock with calcium will raise the pH. Crushed coral also has high levels of calcium, and can raise pH naturally. Dolomite is another rock that will raise pH.

Other Aquarium (and Fish Tank) Rocks We Reviewed

Best Aquarium Rock Overall
Nature's Ocean 12-Inch Coral Base Rocks for Aquarium – 40 Pounds
Nature’s Ocean coral rocks are 100 percent natural aragonite, which can be used as-is or broken down into smaller rocks.

We looked at 20 other aquarium rocks. Even though they didn’t make our 5 best aquarium (and fish tank) rocks list, they’re still great options for your aquarium. The information you need to compare each one is included with the listing.

Mountain Stone for Aquariums

Aqua KT Aquarium Landscape Mountain View Cave Rock

Aqua KT Aquarium Landscape Mountain View Cave Rock

Made from resin, this cave rock features multiple holes for your fish to swim through and hide in.

Key Features:

  • Around 8 inches by 4 inches by 8 inches
  • Smooth surface
  • For freshwater and saltwater

Cost: $19

Exotic Environments Skull Mountain Aquarium Ornament

Exotic Environments Skull Mountain Aquarium Ornament

Made for fresh or saltwater, your fish can swim in and out of, or hide in, this skull mountain.

Key Features:

  • Available in multiple sizes
  • One piece
  • Hand-painted detail

Cost: $17

FEDOUR Aquarium Mountain View Stone Ornament

FEDOUR Aquarium Mountain View Stone Ornament

Made from resin, this decorative rock features real stone color, moss, and small trees.

Key Features:

  • 4 inches by 7 inches
  • Comes with six small artificial plants
  • Suitable for small tanks

Cost: $11

Lifegard Aquatics 25G Smoky Mountain Stone

Lifegard Aquatics 25G Smoky Mountain Stone

This mountain stone kit includes a variety of different size smoky stones. 10-gallon kits are also available.

Key Features:

  • Small stones are about 4 inches by 8 inches
  • Medium stones are 8 inches by 12 inches
  • Large stones are 12 inches by 20 inches

Cost: $49

Coral Rock for Aquariums

ARC Reef Reef Stacker Dry Rock Aquascaping Kit

ARC Reef Reef Stacker Dry Rock Aquascaping Kit

Made for saltwater aquariums, this dry rock kit contains 25 pounds of rock, five connecting rods, and five frag plugs.

Key Features:

  • Calcium carbonate-based
  • No curing needed
  • Sterilized with high-pressure heat

Cost: $80

Caribsea Life Rock

Caribsea Life Rock

Caribsea Life Rock is 40 pounds of aragonite rock that has live bacteria.

Key Features:

  • 50 percent void space
  • Live spored bacteria
  • Made for saltwater

Cost: $158

Carib Sea Aquatics Life Rock Display Box

Carib Sea Aquatics Life Rock Display Box

Create a dry rock formation that is safe for fresh or saltwater.

Key Features:

  • 50 percent void space
  • Live spored bacteria
  • 20 pounds of rock

Cost: $87

Carib Sea South Sea Base Rock 10-Pound

Carib Sea South Sea Base Rock 10-Pound

Good for coral and coralline growth, this aquarium rock can be used in fresh and saltwater.

Key Features:

  • Live rock, no curing needed
  • Assorted sizes and shapes
  • Lightweight and porous

Cost: $36

Dragon or Slate Stone for Aquariums

Aqualexs Aquarium Ohko Dragon Stone Rock

Aqualexs Aquarium Ohko Dragon Stone Rock

Create a dragon stone lair using the different sized rocks by Aqualexs.

Key Features:

  • 5 pounds of .5-inch to 3-inch stones
  • Color will vary
  • Will not affect water chemistry

Cost: $23

Capcouriers Slate Stones

Capcouriers Slate Stones

Use slate stones to create an underwater landscape of caves and varying rock formations.

Key Features:

  • Must rinse before using
  • 2.5 pounds of 2-inch to 3-inch stones
  • About 17 to 20 stones

Cost: $15

Lifegard Aquatics 10G Dragon Rock Kit

Lifegard Aquatics 10G Dragon Rock Kit

Aquascape your aquarium with a dragon rock kit that contains four small rocks and two medium rocks.

Key Features:

  • 25-gallon kit available
  • Small rocks are 3.5 inches by 8 inches
  • Medium rocks are 8 inches by 12 inches

Cost: $32

Natural Aquarium Stones Brown/Grey Slate

Natural Aquarium Stones Brown/Grey Slate

Decorate your aquarium with a mix of gray, brown, and tan slate stones, some with quartz strewn throughout.

Key Features:

  • Sourced by small family USA business
  • 5 pounds of 1-inch to 3-inch stones
  • No two stones are the same

Cost: $23

Natural Slate Stone Rocks for Aquarium

Natural Slate Stone Rocks for Aquarium

This slate stone can be used in aquarium tanks to create an interactive landscape.

Key Features:

  • 2 pounds of 1-inch to 3-inch stones
  • Sourced in the USA
  • Naturally holds heat

Cost: $16

Smooth Rocks for Aquariums

Maynooth Natural Granite Large 3” Granite River Rock

Maynooth Natural Granite Large 3” Granite River Rock

Straight from Canada, these decorative rocks can be used for your aquascaping.

Key Features:

  • Rinse before using
  • 5 pounds of 3-inch rocks
  • About 4 rocks per bag

Cost: $14

Penn-Plax Deco-Replicas Granite Aquarium Ornament Series

Penn-Plax Deco-Replicas Granite Aquarium Ornament Series

Stack and build an interactive underwater environment for your fish with these granite stone cave replicas.

Key Features:

  • Available in different size sets
  • Looks like natural granite
  • Range in size from 2 inches by 2.5 inches to 3.5 inches by 5.5 inches

Cost: $42

Plecoceramics Cichlid Stone Decoration

Plecoceramics Cichlid Stone Decoration

This smooth stone decoration is made from gray clay and provides a hiding space for your cichlid fish.

Key Features:

  • Rinse in freshwater before using
  • For 15 to 50 gallon tanks
  • Roughly 7 inches by 5 inches by 4 inches

Cost: $24

Other Rocks for Aquariums

BCQLI Sphere Bio-Filter Media for Marine and Freshwater Aquariums

BCQLI Sphere Bio-Filter Media for Marine and Freshwater Aquariums

Decorate your freshwater or saltwater aquarium with red volcanic rock.

Key Features:

  • 400 grams of rocks
  • Porous rocks to help filter
  • Rinse before using

Cost: $11

DreamDealsSG Tourmaline Balls for Freshwater Aquarium Tank

DreamDealsSG Tourmaline Balls for Freshwater Aquarium Tank

This organic tourmaline has more than 30 different minerals to help keep your freshwater tank pH balanced.

Key Features:

  • Copper-free
  • Add one ball per gallon
  • 100 pack

Cost: $13

Marina Décor Polyresin Cave

Marina Décor Polyresin Cave

The Marina Décor underwater cavern provides your fish a place to hide.

Key Features:

  • Roughly 5 inches by 11 inches by 8 inches
  • Artificial plants attached
  • Will not affect water chemistry

Cost: $28

SunGrow Mineral Balls Calcium-Rich Tourmaline Balls

SunGrow Mineral Balls Calcium-Rich Tourmaline Balls

Give your tropical fish the minerals it needs, like calcium, boron, iron, and manganese.

Key Features:

  • Soak in water for two hours before using
  • Change every three months
  • Absorbs pollutants and other toxins

Cost: $9

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